The present invention relates to a thin film resistor which is used, for example, as a thermal head heating resistor for a printer or facsimile equipment or a resistor element of a high density wiring board which is mounted in an electronic computer.
A thin film resistor formed from metallic chromium, metallic silicon, or silicon oxide, which has a high heat resistance and power resistance, is indicated in Japanese Patent Application Laid-Open No. 58-84401. Furthermore, a thin film resistor formed from metallic chromium, metallic silicon, silicon oxide, or chromium oxide, which has more improved characteristics than the above thin film resistor, is indicated in Japanese Patent Application Laid-Open No. 59-94393.
In an example indicated in Japanese Patent Application Laid-Open No. 58-84401, as shown in FIG. 1, when a thin film is heated and cooled, chromium and silicon contained in the above thin film combine with each other to form chromium silicide within a temperature range from 350 to 450.degree. C. The resistivity of the thin film increases suddenly as shown by numeral 3 in FIG. 1 as the deposition phenomenon advances.
Therefore, when the above thin film is to be used at high temperatures or applied with high power which may generate heat, the thin film is required to be subjected to heat treatment for sufficient stabilization during production, for example, treatment at 350.degree. C. for one hour.
In FIG. 1, numerals 2, 3, 4, 5, and 6 indicate the path order of resistance changes in the heating and cooling cycle and 1 the minimum value of the above resistance changes. The above phenomenon that the resistivity suddenly increases has an advantage that the resistor element is prevented from overheating by an increase in the resistivity when overpower is applied. There is a problem imposed that this phenomenon advances slowly in the normal operation stat so as to change the resistance. In an example indicated in Japanese Paten Application Laid-Open No. 59-94393, the resistance does not increase because chromium oxide existing in the film suppresses the above phenomenon for forming chromium silicide, a resistor thin film in the usable state can be formed by heat treatment at a comparatively low temperature, and the resistance changes little in the normal operation state. However, there is a problem imposed that care is required for use at a constant voltage because the resistance decreases continuously when overcurrent is applied.